Music synthesis generally operates by taking a control stream input such as a MIDI stream and generating sound associated with that input. MIDI inputs include program change, which selects the instrument to play, note pitch, note velocity, and continuous controllers such as pitch-bend, modulation, volume, and expression. Note velocity and volume (or expression) are indicators of loudness.
All music needs time-varying elements such as attack transients and vibrato to sound natural. An expressive musical synthesizer needs a way to control various aspects of these time-varying elements. An example is the amount of attack transient or the vibrato depth and speed.
A common method of generating realistic sounds is sampling synthesis. Conventional sampling synthesizers use one of two methods to incorporate vibrato. The first sort of method stores a number of recorded sound segments, or notes, that include vibrato in the original recording. Every time the same note is played by such a synthesizer, the vibrato sounds exactly the same because it is part of the recording. This repetitiveness sounds artificial to listeners. The second sort of method stores a number of sound segments without vibrato, and then superimposes artificial amplitude or frequency modulation on top of the segments as they are played back. This method still does not sound natural because the artificial vibrato lacks the complexity of the natural vibrato.
In recent years, synthesizers have adopted more sophisticated methods to add time-varying elements such as transients and vibrato to synthesized music.
U.S. Pat. No. 6,31 6,710 to Lindemann describes a synthesis method which stores segments of recorded sounds, particularly including transitions between musical notes, as well as attack, sustain and release segments. These segments are sequenced and combined to form an output signal. U.S. Pat. No. 6,298,322 to Lindemann describes a synthesis method which uses dominant sinusoids combined with a vector-quantized residual signal. U.S. Pat. No. 6,111,183 to Lindemann describes a synthesizer which models the time-varying spectrum of the synthesized signal based on a probabilistic estimation conditioned to time-varying pitch and loudness inputs. Provisional Application for Patent Ser. No 60/644,598, filed Jan. 18, 2005 by the present inventor describes a method for modeling tonal sounds via critical band additive synthesis.
A need remains in the art for improved methods and apparatus for synthesizing sound in which time-varying elements such as attack transients and vibrato can be controlled in an expressive and realistic manner.